A variety of breathing assistance devices, which we will also generally refer to as “respirators” in this text, are available today. These respirators are equipped with a source of respiratory pressurized gas. They are generally referred to as “autonomous” because an external pressurized gas feeding is not required to operate them. These devices provide the patient, at each inspiration, with a respiratory gas (typically ambient air to which a complementary gas such as oxygen can be added).
Different types of respirators are known. These different types of respirators can be classified according to their size, because the size of these devices is an important parameter. It is generally desirable to minimize the size of the respirator in order to facilitate the operation of the respirator in multiple different locations, for instance, at home as well as in the hospital. In addition, smaller sized respirators tend to increase the mobility of the patient.
Non-Transportable Respirators
A first type of respirator is generally referred to as a non-transportable respirator. A non-transportable respirator is schematically illustrated in FIGS. 1a to 1d. Such devices are generally equipped with a respiratory gas source S1 having a very large size and/or weight. This gas source can be internal to the device, or external to the device. The source of gas S1 is commonly coupled to the patient P through two ducts, however, a single duct may be used. An inspiration duct 11 is dedicated to the inspiration phase, and it carries pressurized gas from the source of gas to the patient P during inspiration. An expiration duct 12 is dedicated to the expiration phase, and it carries expiratory gases, such as carbon dioxide, which are exhaled by the patient during the expiration phase.
These non-transportable respirators are further provided with an inspiratory valve 13 and an expiratory valve 14. These two valves are located close to the gas source S1 on the inspiration duct 11 and on the expiration duct 12, respectively. The inspiratory valve 13 controls the flux of the pressurized gas transmitted to the patient during the respiratory phases. The expiratory valve 14 allows the expiratory gases of the patient to pass out of the expiratory duct 12, and into the surrounding atmosphere. The expiratory valve can be controlled based on a Positive End Expiratory Pressure (PEEP) control scheme.
Most of the operating modes of the respirators require monitoring of the expiratory gas flow and/or expiratory pressure. Therefore one or more sensors 19 for sensing the gas flow and/or pressure are located in the expiration duct 12. Each sensor usually needs to be connected to the central unit 10 of the respirator by at least three wires, in order to be supplied with power and to convey data. Therefore the sensors 19 are generally located near the gas source S1 in order to avoid further increasing the complexity of the already quite complex and large double transmission circuit by the addition of sensors and wires. Both the inspiratory and expiratory valves require specific and often complex control systems, usually in the form of a processor or controller 15, which is coupled to or otherwise in communication with the valves and the sensor 19.
Non-transportable respirators are generally provided with relatively long ducts, typically of about 150 to 180 cm. This configuration results in a high breathing resistance, which increases the work of breathing for the patient. Indeed, if the expiratory valve 14 is located at the end of the expiration duct 12 near the gas source S1 (the “distal end”), and the expiration duct 12 is relatively long, the patient P will need to “push” his expiration through the expiration duct 12 until the expired air reaches the expiration valve 14 wherein it is vented to the atmosphere.
When connected to a non-transportable respirator, the patient P will always be able to expire through the expiration duct 12, even if the gas source S1 is disabled, as shown in FIG. 1d. During expiration, the positive pressure of the expiratory gases will cause a safety backflow valve 16 on the inspiration duct 11 to close, and the expiration valve 14 on the expiration duct 12 to open. Thus, the patient will be able to expel expiration gases.
Also, if the gas source S1 is disabled, the patient will be able to draw in atmospheric gases through the inspiration duct 11. As shown in FIG. 1c, during the inspiration phase, the patient will be able to draw in atmospheric gas through the safety back flow valve 16 on the inspiration duct, and the expiration valve 14 on the expiration duct 12 will be closed. The safety back flow stop valve 16 is not located on the expiration duct 12 because it would be dangerous for the patient P to inspire through the expiratory duct 12, which usually contains expired carbon dioxide.
Transportable Respirators
A second type of respirator can be referred to as transportable respirators. A transportable respirator is schematically illustrated in FIGS. 2a to 2d. This transportable respirator is provided with a central unit 20 comprising an internal respiratory gas source S2. The gas source S2 may be a small turbine or blower, having optimized characteristics in order to limit the volume occupied by the device.
These transportable respirators typically use a single gas transmission duct 21 between the source S2 and the patient P, in contrast with devices having two ducts (an inspiration duct and an expiration duct). The respirators use an expiratory valve 22 located on the single duct 21, near the patient P (i.e. at the proximal end of the duct). In contrast to the above-described non-transportable respirators, the proximal location of the expiratory valve 22 eliminates the breathing resistance phenomenon during the expiratory phase which is caused by the length of the duct in a non-transportable respirator between the patient and the expiratory valve.
In typical transportable respirators, as illustrated in FIGS. 2a to 2d, the expiratory valve 22 is a pneumatic valve that is operated by a pressurized air feeding conduit 23, coupled between the respiratory gas source S2 (or to another source of pressure such as an independent micro-blower) and an obstructing cuff 24 of the expiratory valve 22. The pressure from the gas source S2 inflates the obstructing cuff 24 during the inspiration phase to ensure that the gas traveling along the transmission duct 21 is delivered to the patient P.
The control of the expiratory valve thus requires a second conduit 23, which obviously limits the miniaturization of the respirator, particularly the breathing circuit. During the expiration phase, the expiratory valve 24 is either opened or partially closed in order to establish a positive end expiratory pressure (PEEP) in the gas transmission duct to balance the residual overpressure in the patient lungs. In order to establish such a PEEP, it is necessary to control, very precisely, the pneumatic inflating pressure of the cuff 24 of the expiratory valve 22. This increases the complexity of the controller 25 of the respirator.
In some respiratory modes, the expiratory valve 22 has to be operated as much as possible in real time, which is quite difficult in such expiratory valves because of the pneumatic inertias which are associated with them. Moreover the configuration of such a known respirator imposes a limitation of the value of the PEEP at around 20 cmH2O, while some respiratory modes would need a higher value of the PEEP (e.g. 40 cmH2O or even more).
For the same reason as for non-transportable respirators, the expiratory gas flow and/or expiratory pressure may have to be controlled, and thus gas flow and/or pressure sensors 29 will typically be provided near the expiratory valve 22. Here again, this requires providing wires along the gas transmission duct 21 between the central unit 20 and the patient P. Usually three wires (two for power supply and one for data transmission) are provided for each pressure sensor and each gas flow sensor. Since expiratory gas flow and pressure generally have to be measured, a connection cable 26 of at least five wires is thus required between the central unit 20 and the expiratory valve 22 at the proximal end of the device.
In order for the patient to safely use such a transportable respirator, the device must allow the patient to breathe in any situation, including if the pressurized gas source is disabled. With a respirator having a single gas transmission duct 21 and a separate conduit 23 for pneumatic control of the expiratory valve 22, the patient P can always expire through the pneumatic expiratory valve 22, even if the pneumatic feeding of the expiratory valve 22 is disabled, as shown in FIG. 2d. Indeed, if the pneumatic feeding of the expiratory valve is disabled, which would be the case when the gas source is disabled, the cuff 24 of the expiratory valve 22 will not be inflated, and the patient P will be able to expire expiratory gases EP through the expiratory valve 22. In such case, it will be impossible for the patient P to inspire through this pneumatic expiratory valve 22, since the cuff 24 will obstruct the passage. However, the patient P will be able to inspire via the safety back flow stop valve 27 located on the inspiration conduit 21, as shown in FIG. 2c. As shown in FIG. 2a, this safety valve 27 will normally be closed under the effect of the pressure feeding Gs coming from the gas source S2. But if the gas source S2 is disabled, the pressure of the patient inspiration IP will open the safety valve 27, allowing the patient P to inspire air from outside, as illustrated in FIG. 2c. 
In order to allow a safe inspiration through the safety valve 27 and the whole length of the duct 21, the diameter of the duct must be relatively large. There are generally pressure loss standard requirements to fulfill for addressing this issue of safety. For example, the French standards state that the maximum pressure loss between the source and the patient must not exceed 6 hPa for 1 liter/second for an adult and 6 hPa for 0.5 liter/second for a child. In order to fulfill these requirements, the transmission duct of typical devices as illustrated in FIGS. 2a to 2d must have a minimum diameter of 22 mm for an adult, and a minimum diameter of 15 mm for a child. The requirement for such large diameter ducts is an obstacle to miniaturization of the device, particularly the breathing circuit.
For the same reasons as for the transportable respirators, the diameters of the ducts on the non-transportable respirators illustrated in FIGS. 1a-1d must be relatively large to fulfill the pressure loss requirements. That is, the ducts must have a diameter of at least 15 mm for children and 22 mm for adults in order to allow a safe inspiration through the safety valve 16. And here again, such large duct diameters is an obstacle to miniaturization.
The pathologies and diseases to be treated by the above-described respirators are varied, and the breathing assistance devices can therefore be of different types. The respirators can be pressure-controlled or volumetric-controlled, and they can be operated according to different operating modes. Each operating mode is defined by particular setting and checking variables, but also by a particular type of material.
Some respirators, which can be referred to as hybrid respirators, are able to work according to several operating modes. However their material configuration, in particular the accessories (such as the type of ducts between the gas source and the patient, the presence of an expiratory valve, the use of a mask with apertures, etc.), must be adapted to the chosen operating mode.
It would be desirable to allow a single device to operate according to a large variety of modes, without requiring that the device be modified for each mode, such as by adapting its ducts, accessories, etc.